Process of tawing hides or skins



UNI-TED STATES PATENT OFFICE,

IIERMANN DANNENBAUM, OF PHILADELPHIA, PENNSYLVANIA.

PROCESS OF TAWING HIDES OR SKINS, 80C.

SPECIFICATION forming part of Letters Patent No. 613,898, dated November 8, 1898.

Application filed January 29; 1898. fierial Noi 668,478. (No specimens.)

To aZZ whom it may concern:

Be it known that I, HERMANN DANNENBAUM, a citizen of the United States, residing in the city and county of Philadelphia, State of Pennsylvania, have invented a new and useful Improvement in Processes of Tawing Hides or Skins,which improvement is fully set forth in the following specification and accompanying drawings. p

The invention is designed more particularly for reducing the chromic acid in hides and skins which have been tanned with such chromic acid or chromic-acid salts by the action of a nitrous-acid compound, such as nitrite of soda,inthe presence of an acid,whereby after subsequent usual treatment leather is produced which is durable, strong, and waterproof.

While hides and skins may be converted into leather by the action of chromic acid or chromic-acid salts alone, leather made in this Way is not waterproof and only will become so when the chromic acid is reduced in the skin into chromic oxid.

In treating hides or skins which have been tanned with chromic acid or chromic-acid salts with a solution of a nitrous-acid salt in the presence of an acid the chromic acid is reduced to chromic oxid, which unites with the fiber of the skins, producing leather that out and drained, and after the surplus solu= tion is pressed out they are transferred to the second bath, which is prepared by dissolving about four per cent. of the Weight of the skins of nitrite of soda in water. After the skins are in this bath I add to it a quantity, sufficient to decompose the entire amount of nitrite of soda, of oil of vitriol, or any other acid, suitably diluted. This requires from one-half to one pound of oil of vitriol to one pound of nitrite. The nitrous anhydrid and other products of decomposition which are thus formed act immediatelyupon the chromic acid and reduce the same to chromic oxid. In order to obtain an equal reduction, it is desirable to agitate the hides or skins in the solution, and they remain therein until the chromic acid has been sufficiently reduced. The hides or skins are then removed from the solution and drained, after which in order to remove any free acid in the hides and skins they are washed in a weak alkaline solution, for which I prefer to use carbonate of soda or borax or both. The surplus water is then pressed from the skins, and the latter are finished in the usual manner.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is

The process of tawing hides or skins,which consists in subjecting the previously-prepared hides or. skins to the action of asolution of a chromi'c-acid salt, such as bichromate of potash, in the presence of an acid, such as mu.- riatic acid, and then subjecting said hides or skins to the action of a'solution of a nitrousacid salt, such as nitrite of soda, in the presence of an acid, substantially as described.

HERMANN DANNENBAUM.

Witnesses:

JOHN A. WIEDERsHEIM, WM. 0. WIEDERSHEIM. 

